1. Field of the Invention
The present invention concerns a system for monitoring a quench tube of a superconducting magnet in a magnetic resonance tomography apparatus (MRT apparatus).
2. Description of the Prior Art
In medical imaging MRT apparatuses have increasingly gained importance in recent years. In order produce images with such apparatuses, typically different magnetic fields that are matched to one another in terms of spatial and temporal characteristics are combined with one another. One of these magnetic fields is a static magnetic field with a high field strength of typically 1.5 to 3 Tesla. In order to generate such high field strengths, usually superconducting magnets are used with conductor wires formed by a superconducting material, for example a niobium-titanium alloy. The cooling of the conductor wires and the maintenance of the superconducting state ensue with liquid helium.
In a superconducting magnet on rare occasions an event known as a quench occurs. Various causes can lead to the situation that the superconducting state of the conductor wire changing into the normally-conductive state. The resulting severe heating of the conductor wire leads to a sudden vaporization of the liquid helium. In order to prevent damage to the apparatus, the large volume of helium gas suddenly created must be quickly directed away from the apparatus. In MRT apparatuses with a superconducting magnet this ensues by means of what is known as a quench tube through which the helium gas is conducted away from the apparatus into the ambient atmosphere. The diameter of such a tube is calculated dependent on its length and its curvatures and is typically 20 to 40 cm. The quench tube can never be blocked or leaky during the long-term operation of an MRT apparatus, otherwise the housing of the MRT apparatus could be damaged (even an explosion) given a quench or the building could be flooded with helium (possible asphyxiation danger).
A ventilation tube arrangement for a superconducting magnet system is known from DE 696 34 719 T2, which arrangement also serves as a flow path in the case of a magnet quench.
A quench tube can be damaged by multiple causes. Animals or plants can penetrate into the quench tube via the opening discharge to the atmosphere or discharge the opening. Also, water can accumulate in the quench tube over the course of many years of operation, for example as condensation water that forms after tanking up the magnet reservoir with liquid helium (the cold helium exhaust thereby created is directed through the quench tube) or in the case of disadvantageous weather conditions, or as rainwater that can penetrate the discharge opening in the case of faulty mounting. The quench tube can thereby be damaged. Upon a quench the water located in the quench tube represents a significant problem since it can be frozen by the very cold helium gas and thus block or even burst the tube.
Quench tubes are regularly checked by an overview during maintenance tasks. Since an intact quench tube is an important, safety-relevant component but not an operationally-relevant component of an MRT apparatus, it can occur that the quench tube is only insufficiently checked in the maintenance, particularly since the quench tube is often not accessible over its entire length. Possible blockages or damages that are caused by penetrating foreign bodies can easily be overlooked, or not detected at all if maintenance intervals that are too long.
A method for space monitoring and a space monitoring system for traffic spaces (in particular tunnel regions) for situation recognition by means of evaluation of video signals is known from DE 103 41 426 A1. The system includes illumination units and image acquisition units (CCD cameras).